FeX2 or FeX3 (X = Cl ≫ Br) alone or with P ≫ X > O > N > C ligands and bromoester initiators enable the successful ATRP of butadiene in toluene at 110 °C.

Despite over two decades of research, butadiene (BD) remains one of the most challenging monomers for atom transfer radical polymerization (ATRP). A comprehensive mechanistic investigation of the effect of the reaction parameters (initiator structure, halide, Cu catalyst, ligand, solvent, temperature, reagent ratios, ATRP method, etc.) on the polymerization outcome (kinetics, dependence of the molecular weight (M n ), polydispersity (PDI), and halide chain end functionality (CEF) on conversion) affords a quantitative understanding of diene ATRP and reveals that despite drawbacks such as low boiling point, Diels−Alder dimerization, a very low polymerization rate, and especially, a very weak and side-reaction-prone allyl halide chain end, a rational selection of the polymerization conditions (normal-or ICAR (initiators for continuous activator regeneration)-ATRP, tertiary bromoester initiators, low nucleophilicity ligands including bipyridyl, nonpolar solvents such as toluene at 110−130 °C), still enables the synthesis of welldefined polybutadiene (PBD) with a wide range of M n values (1000−100000), low PDIs (1.3−1.5) and high Br-CEFs (>90%), suitable for the synthesis of complex architectures including star PBD and ABA triblock copolymers with styrene and methyl methacrylate.

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